The pathophysiology of chronic muscle pain associated with temporomanibular disorders is still poorly understood. This research will elucidate the importance of peripheral receptor mechanisms in craniofacial muscle pain and hyperalgesia. Specifically, we propose that peripheral excitatory amino acid (EAA) and neurokinin (NK) receptors are critical components in inducing neuroplastic changes in central trigeminal neurons and the development of muscle hyperalgesia. To investigate our proposal, two research aims are constructed, each with several working hypotheses. We will use behavioral, immunocytochemical and electrophysiological approaches to test these hypotheses. In Aim 1, we will study the contribution of peripheral EAA receptors for the generation of central sensitization and muscle hyperalgesia. Specific hypotheses under this Aim are (1) Blockade of peripheral NMDA and non-NMDA glutamate receptors differentially affect neuronal activation in the Vc under an experimental myositis condition, (2) Intramuscular injections with glutamate will induce central sensitization ofVc neurons and antagonizing peripheral EAA receptors-will prevent the glutamate-induced sensitization, (3) Blockade of peripheral EAA receptors will significantly reduce muscle pain and hyperalgesia following experimental myositis. In Aim 2, we will study (a) the contribution of peripheral neurokinin receptors for the generation of central sensitization and muscle hyperalgesia, and (b) the interaction between peripheral EAA and NK receptors in generation of muscle hyperalgesia. Specific hypotheses are (4) Blockade ofNKl or NK2 receptor will differentially affect the inflammation^inducedneuronal activation in the Vc, (5) Local treatment with NK1 or NK2 receptor antagonist will prevent the, inflammation-induced sensitization of Vc neurons, (6) Blockade of peripheral NKl or NK2 receptor will significantly reduce the inflammation-induced muscle hyperalgesia, (7) Blockade of both peripheral EAA and NK receptors will reduce the inflammation-induced c-fos expression in the Vc greater than that produced by the blockade of each receptor type only, and (8) Blockade of both peripheral EAA and NK receptors will reduce the muscle hyperalgesia greater than that produced by the blockade of each receptor type only. These studies will contribute to understanding the pathophysiology of chronic orofacial muscle pain and provide direct insights for the development of new treatment modalities.